The Coronae of F-K Dwarfs: Factors Controlling Their Properties
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**Session 38 -- EUVE -- Astronomy II**
*Oral presentation, Tuesday, 2:00-6:30, Zellerbach Auditorium Room*

## [38.06] The Coronae of F-K Dwarfs: Factors Controlling Their Properties

*C. Jordan (U. of Oxford)*
X-ray observations of late-type stars can be used to determine
average coronal emission measures, Em(T$_c$), and temperature,
T$_c$, provided the spectra can be fitted adequately by single
temperatures. Em(T$_c$) and T$_c$ can be correlated with stellar
properties, such as the rotation period, or with convection zone
parameters, such as the Rossby number (Ro = P(rot)/turnover time at
the base of the convection zone). Including F to K dwarfs, the
closest correlations are found between Em(T$_c$) g$\cdot
^{\frac{1}{2}}$ and Ro, and T$_c$ g$\cdot ^{\frac{1}{2}}$ and Ro.
The total energy losses from the coronae (radiation plus thermal conduction)
can, with some assumptions, also be expressed in terms of Em(T$_c$)
and T$_c$. These total losses, and hence the non-thermal energy required to
heat the corona, scale approximately as Ro$^{-1}$. The coronal magnetic
field can also be expressed in terms of Em(T$_c$) and T$_c$, through the
pressure and plasma Beta, and comparisons can be made with specific heating
mechanisms. Some recent results will be presented, including the relation
between these implied coronal fields and surface magnetic fields and filling
factors. The contribution from new observations with ROSAT, and expected
from EUVE, will be discussed.

This work has been supported by the SERC through grant GR/H25539.

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